Measuring device for measuring the state of oils or fats

ABSTRACT

A measuring device is used to measure the state of a liquid product which is to be measured, in particular oil or fat. Said measuring device comprises a housing, a hollow connecting element which is secured therein and a carrier which is applied to the opposite end of the connecting element, said carrier being used to receive a sensor which can be used to measure the electric property of a product which is to be measured. The sensor is in contact with the measuring unit by means of at least one electric line, which is arranged in the region of the housing and/or with the end of the connecting element oriented towards the housing. The measuring device comprises means which can be used to minimize the falsifying effect of the water content in the product, which is to be measured, on the measuring result.

TECHNICAL FIELD

The present application relates to a measuring device for measuring thestate of oils or fats.

BACKGROUND OF THE INVENTION

Hot oils or fats are often used not only once, but are utilized in deepfryers over a longer period for successively preparing different foods.The oil or fat is decomposed by oxidation at the hot operatingtemperatures between approximately 120° C. and 180° C. and undesirablechemical products such as free fatty acids and polymers are formed,which not only impair the taste, but may also have adverse healtheffects.

In order to avoid replacing frying oils or fats too early or too late,measuring devices are used for measuring the state of oils or fats,including tests for their electrical properties. Measuring thedielectric constant, which is a reliable measure of the degree ofdecomposition of fats or oils, is particularly suitable.

EP 1 046 908 A2, for example, describes a measuring device for measuringthe state of an oil or fat, which has a housing which contains theelectronic analyzer units and a data display, as well as a tubularconnecting element with a sensor situated at its tip which may bedirectly immersed into the hot oil or fat and is suitable fordetermining the dielectric constant. The sensor and the electronicanalyzer circuit are electrically connected via a cable laid freelywithin the connecting element.

DE 101 63 760 A1 describes a refinement of the above-mentioned measuringdevice. In the measuring device presented therein, the electricalconductors between the sensor and the electronic analyzer circuit areformed by metallic conductors printed on a ceramic substrate. Thetubular connecting element is shaped in such a way that it surroundsmost of the substrate and narrows downward in such a way that only thearea of the substrate on which the sensor is situated is accessible fromthe outside. An insulating sealing adhesive is introduced and curedbetween the substrate and the connecting element, so that there is noelectrical connection between the connecting element and the electricalconductors. In addition, a temperature-stable seal is achieved, whichprevents the oil from penetrating inside the connecting element. Atemperature sensor may also be provided, whose measurement results mayalso be processed by the electronic analyzer circuit.

The disadvantage of this measuring device is that the measured valuesare often greater than the actual values despite the use of reliablesensors and suitable electronic analyzer circuits.

Accordingly, it is desirable to provide a measuring device that woulddeliver more accurate and more reliable measurement results.

SUMMARY OF THE INVENTION

The present invention is based on the finding that during frying largeamounts of water are expelled from the fried items, part of whichtemporarily remains in the frying oil. Since the dielectric constant ofwater is approximately 20 times greater than that of the frying oil,even small amounts of water result in high measured values. Depending onthe age and temperature of the oil, it may take between 5 minutes (freshoil and high temperature) and 30 minutes (old oil and low temperature)until the influence of the water has dropped to a tolerable value andthe measured value coincides with the actual value of the oil.

According to the present invention, the measuring device has means whichare suitable for minimizing the distorting influence of the watercontent in the oil or fat to be measured on the measurement result,making the measurement result considerably more accurate.

The means preferably include a moisture sensor, which is situated in thearea of the measuring device to be immersed. It is thus reliablydetermined whether the oil contains even small amounts of water.

In another embodiment, the means include an electronic circuit fordetermining the complex impedance and the phase angle of the dielectricconstant, providing information which essentially correlates with thewater content of the oil. This allows the distorting influence due towater to be distinguished from the influence due to ageing of the oilusing a single sensor.

In a further embodiment, the means have a device for filtering the oilor fat to be measured, which surrounds the sensor substrate fordetermining the dielectric constant. Such a device ensures that only oilfrom which the residual moisture has been removed by the drying filterdevice reaches the sensor.

The measuring device advantageously also has a temperature sensor whichprovides additional information for making the determination of thestate of the oil or fat to be measured more accurate.

Further properties, features, and advantages of the present inventionare derived from the description that follows and the appended drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the system are described with reference to the severalfigures of the drawings, in which:

FIG. 1 shows a measuring device according to an embodiment of thepresent invention in a front view;

FIG. 2 shows an enlarged front view of the lower area, to be immersed,of the measuring device of FIG. 1;

FIG. 3 shows an enlarged rear view of the lower area, to be immersed, ofthe measuring device of FIG. 1;

FIG. 4 shows an enlarged rear view of a variant of the lower area, to beimmersed, of the measuring device of FIG. 1, and

FIG. 5 shows an enlarged front view of the lower area, to be immersed,of a variant of the measuring device.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Referring now to the figures of the drawings, the figures comprise partof this specification and illustrate exemplary embodiments of thedescribed system. It is to be understood that in some instances variousaspects of the system may be shown schematically or may be exaggeratedor altered to facilitate an understanding of the system.

FIG. 1 shows a measuring device 1 according to the present invention formeasuring the state of oils or fats, which has a housing 3 in its upperarea. The housing has a display 5 for displaying measured values. Thedisplay is preferably designed as an LCD display and is switchablebetween graphic display, e.g., color coding of the measured values, andnumerical display. A keyboard 7 is provided for inputting controlinstructions, via which instructions may be issued to the centralcontrol unit (not shown). Keyboard 7 is preferably designed as amembrane keyboard. The housing may preferably also have an interface 9,which may be used for communication with external computers. Measuringdevice 1 is preferably designed to be self-adjusting. During the use ofmeasuring device 1, housing 3 is simultaneously used as a handle for theoperator.

A hollow connecting element 10, which is sufficiently long and is madeof a material with poor thermal conductivity, protrudes downward fromhousing 3, so that the sensitive electronic analyzer circuit (not shown)of measuring device 1, which is situated in the area of housing 3 and/orin the area of connecting element 10 facing housing 3, is adequatelyprotected against the heat of the oil or fat to be measured. Thesemeasures ensure that the operator is able to safely perform themeasurements. Connecting element 10 is preferably made of stainlesssteel, which, in addition to its poor thermal conductivity, is alsosuitable because of its unrestricted applicability in the food industry.Connecting element 10 is preferably designed as a tubular component andis suitable for receiving electrical conductors 12 running insideconnecting element 10. Electrical conductors 12 are situated on at leastone flat substrate 14 which is characterized by its electricalinsulating properties, for example, on a substrate 14 made of a ceramicmaterial.

In the lower area of first substrate 14, there is a sensor 16 formeasuring electrical properties of the oil or fat and, preferably, atemperature sensor 18, whose measured values are conducted viaelectrical conductors 12 on substrate 14 to the electronic analyzercircuit. A protective means 20 for protecting sensors 16, 18 againstexternal influences, in particular against contact with the bottom orthe walls of the measuring container, may be applied to the lower areaof substrate 14. In the present case, protective means 20 is designed asa peripheral edge of flat substrate 14, connected to connecting element10.

The gap between substrate 14 and connecting element 10 is insulatinglysealed via suitable sealants (not shown). In the lower end area ofconnecting element 10, a suitable adhesive, for example, a siliconeadhesive, is injected into the gap between substrate 14 and connectingelement 10, so that these are not in direct contact and thus areinsulated from one another. At the same time, the adhesive functions asa seal of connecting element 10, so that no oil or fat is able topenetrate into the inside of connecting element 10. The adhesive surfacemust reliably prevent water inclusions; otherwise an explosion risk, aswell as contamination of the oil or fat to be measured, may result.Substrate 14 as a single-piece element may extend to the electronicanalyzer circuit; it may, however, also be isolated by placing aplurality of substrate sections together in a row via suitableconductive connecting means. This arrangement provides specialadvantages regarding the heat load on the electronic analyzer circuit.

FIG. 2 shows an enlarged view of the lower sections of connectingelement 10 and of substrate 14, which are suitable for being immersedinto the liquid to be measured. Sensor 16 for measuring the dielectricconstant has a capacitor which measures the dielectric constant of theoil. It is preferably designed as an interdigital capacitor which hasfine intermeshing metal conductors, each of which continues as anelectrical conductor 12 leading to the electronic analyzer circuit.Conductors 12 may be made of a fine plating of gold or copper onsubstrate 14, the plating being printed directly onto the ceramiccomponent. A multilayer construction of substrate 14 is alsoconceivable, which may better protect conductors 12 againstenvironmental influences.

Temperature sensor 18 is designed, for example, as an electricalresistor, which may be made of platinum, for example, or anothersuitable material. Temperature sensor 18 may also be situated on theopposite side of substrate 14 in the area of the tip of substrate 14,which makes it possible to further reduce the size of the measuringdevice, while exposing both sensors 16, 18 to the same ambienttemperature.

As is apparent from FIG. 3, a moisture sensor 25 for measuring theresidual moisture in the oil is situated on the back side of substrate14. Moisture sensor 25 is also connected to the electronic analyzercircuit via conductors 12; the electronic analyzer circuit uses thesignals delivered by moisture sensor 25 for correcting the measuredvalues of sensor 16. A polymer sensor is preferably used as moisturesensor 25. The entire lower area of measuring device 1 may be surroundedby a tubular sleeve (not shown) in this arrangement. It is alsoconceivable to position moisture sensor 25 in the area to be immersedoutside connecting element 10.

In the specific embodiment shown in FIG. 4, two moisture sensors 25 a,25 b are applied to connecting element 10, lower moisture sensor 25 abeing positioned near the surface of the oil or fat to be measured andregistering the moisture rising therefrom, while upper moisture sensor25 b is situated at a greater distance from the surface of the oil orfat to be measured. Here it measures the ambient moisture, and thedifference between the measured values of the two sensors 25 a and 25 bis a measure of the water content in the oil or fat to be measured.

As an alternative, as FIG. 5 shows, a filtering device 30 for filteringthe water content out of the oil or fat to be measured may be situatedaround the lower area, to be immersed, of measuring device 1. Anoil-permeable water-retaining filter, which is preferably designed as areplaceable attachment, is suitable for this purpose.

It is also possible to determine the complex impedance and the phaseangle of the dielectric constant using an essentially known electroniccircuit. This provides information which essentially correlates with thewater content of the oil, making it possible to make a distinctionbetween the distorting influence due to water and the influence due toageing of the oil.

The measuring device according to the present invention may also havemeans for compensating the measuring errors in the measuring signaland/or a display device which provides an appropriate visual and/oracoustic signal in the event of increased water content.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1. A measuring device for measuring the state of oils or fats,comprising: a housing; a hollow connecting element attached to thehousing; a substrate mounted on an opposite end of the connectingelement for receiving a sensor for measuring an electrical property ofoil or fat to be measured, the sensor being connected to an electronicanalyzer circuit via at least one electrical conductor, the electronicanalyzer circuit being situated in an area of at least one of thehousing and an end of the connecting element facing the housing; andmeans for minimizing a distorting influence of water content in the oilor fat to be measured on a measurement result, wherein the means forminimizing the distorting influence of the water content includes atleast one moisture sensor.
 2. The measuring device as recited in claim1, wherein the means for minimizing the distorting influence of thewater content includes two moisture sensors, one of which is positionednear the surface of the oil or fat to be measured and is not immersed inthe oil or fat and the other one is situated near the housing formeasuring the ambient moisture.
 3. The measuring device as recited inclaim 1, wherein the at least one moisture sensor is a polymer-basedsensor.
 4. The measuring device as recited in claim 1, wherein the meansfor minimizing the distorting influence of the water content includes atleast one electronic circuit for determining a complex impedance and aphase angle of a dielectric constant.
 5. The measuring device as recitedin claim 1, wherein the means for minimizing the distorting influence ofthe water content includes a device surrounding the substrate of thesensor for filtering the oil or fat to be measured.
 6. The measuringdevice as in claim 1 further comprising: a temperature sensor.
 7. Themeasuring device as recited in claim 1, wherein the oil or fat is afrying oil or frying fat.
 8. The measuring device as recited in claim 1,wherein the means for minimizing the distorting influence of the watercontent analyzes a drift in the measurement result.
 9. The measuringdevice as recited in claim 1, wherein the means for minimizing thedistorting influence of the water content includes means forcompensating for measurement error in a measuring signal.
 10. Themeasuring device as recited in claim 1, wherein the means for minimizingthe distorting influence of the water content includes a display devicewhich provides an appropriate visual or acoustic signal in the event ofan increased water content.
 11. The measuring device as recited in claim1, wherein the means for minimizing the distorting influence of thewater content includes: at least one moisture sensor; means forcompensating measurement error in a measuring signal from the sensor; atleast one electronic circuit for determining a complex impedance and aphase angle of the measuring signal; and a display device which providesan appropriate visual or acoustic signal in the event of an increasedwater content.
 12. A measuring device measuring the state of oils orfats, comprising: a housing; a hollow connecting element attached to thehousing; a substrate mounted on an opposite end of the connectingelement for receiving a sensor for measuring an electrical property ofoil or fat to be measured, the sensor being connected to an electronicanalyzer circuit via at least one electrical conductor, the electronicanalyzer circuit being situated in an area of at least one of thehousing and an end of the connecting element facing the housing; andmeans for minimizing a distorting influence of water content in the oilor fat to be measured on a measurement result, wherein a signal from thesensor is evaluated with the aid of an electronic circuit, both anelectrical property of the oil and the water content in the oil beingdetected by separating a complex impedance of the signal into real andimaginary portions.
 13. A measuring device for measuring the state ofoils or fats, comprising: a housing; at least one sensor for measuring aproperty of oil or fat to be measured, wherein the at least one sensoroutputs a measurement signal; a device for addressing a distortinginfluence of water content in the oil or fat to be measured on themeasurement signal, wherein the device outputs a correction signal; andan analyzer circuit coupled to the sensor and the device for addressinga distorting influence of the water content in the oil or fat, theanalyzer circuit being disposed in an area of the housing, wherein theanalyzer circuit adjusts the measurement signal from the at least onesensor based on the correction signal from the device for addressing thedistorting influence of the water content in the oil or fat.
 14. Themeasuring device as recited in claim 13, wherein the device foraddressing the distorting influence of the water content in the oil orfat includes a moisture sensor.
 15. The measuring device as recited inclaim 13, wherein the at least one sensor includes a sensor formeasuring electrical properties of the oil or fat.
 16. The measuringdevice as recited in claim 13, wherein the at least one sensor includesa temperature sensor.
 17. The measuring device as recited in claim 13,wherein the at least one sensor includes two sensors: a sensor formeasuring electrical properties of the oil or fat and a temperaturesensor.
 18. The measuring device as recited in claim 13, furthercomprising: a display attached to the housing and coupled to theanalyzer circuit.
 19. The measuring device as recited in claim 13,wherein the analyzer circuit determines a complex impedance and a phaseangle of measurement signal.